Friday, December 7, 2012

Life thrives in one of Earth's most extreme environments

Lake Vida in the McMurdo Dry Valleys, in East Antarctica

Here's another story about an ice-entombed Antarctic lake, which I found in New Scientist, 26 November.

It's Lake Vida in East Antarctica, which has been buried for 2,800 years under 20 metres of ice. (But no snow ... weird ... I never knew Antarctica looked like this.) Those figures are negligible compared to much older, deeper lakes under investigation in Antarctica, most notably lakes Vostok and Ellsworth, which I wrote about a couple of days ago. Those are 3 kilometres down and may have been isolated for millions rather than thousands of years.

But here's the interesting bit. Lake Vida is one of the most extreme environments on Earth. It's seven times as salty as the sea, pitch dark, and 13 degrees below freezing, yet despite all this it teems with life.

We were pondering the chance that extraterrestrial life might exist on planets such as Mars, or icy moons such as Jupiter's Europa. The discovery of strange, abundant bacteria in a completely sealed, sunless, salty, icebound lake must strengthen this possibility.

New Scientist quotesPeter Doran of the University of Illinois saying "Lake Vida is a model of what happens when you try to freeze a lake solid, and this is the same fate that any lakes on Mars would have gone through as the planet turned colder from a watery past. Any Martian water bodies that did form would have gone through this Vida stage before freezing solid, entombing the evidence of the past ecosystem." Doran is co-leader of a team working in the Dry Valleys of Antarctica where Vida is situated.

Energy from chemicals not sunlight?

The Vida bacteria belong to previously unknown species. It's thought they probably survive by metabolising the abundant hydrogen and oxides of nitrogen that Vida's salty, oxygen-free water has been found to contain. It seems researchers were surprised to find such high concentrations of hydrogen, nitrous oxide and carbon in the water. They speculate that these chemicals might originate from reactions between salt and nitrogen-containing minerals in the surrounding rock. Over the centuries, bacteria denied sunlight may have evolved to be completely reliant on these chemicals for energy.

Some of the extracted cells are being
grown in a lab, in order to better understand the physical or chemical
extremes they can tolerate. Here's how the researchers think the lake got so salty. As the top and edges of the lake progressively froze, all the salt became concentrated in the remaining water, which as a result can stay liquid below -13 °C.